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GROUND PROXIMITY WARNING SYSTEM - DESCRIPTION AND OPERATION
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1. General (Fig. 1)
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A. The ground proximity warning system (GPWS) provides the pilots with aural and visual warning of potentially dangerous flight paths relative to the ground. The GPWS processes radio altitude information from the No. 1 low range radio altimeter (LRRA), mach signal and altitude rate information from the central air data computer (CADC), glide slope deviation information from VOR/ILS system, and landing gear and landing flap position signals to provide warnings of the following hazards:
(1)
Excessive rate of descent (Mode 1)
(2)
Level flight or too shallow climb towards rising terrain (Mode 2)
(3)
Takeoff altitude loss (Mode 3)
(4)
Unsafe terrain clearance (Mode 4)
(5)
Excessive deviation below the glide slope (Mode 5)
B. The GPWS consists of a ground proximity warning computer, a warning light labeled GPWS, a test switch, a glide slope advisory light labeled BELOW G/S, and an inhibit switch labeled PUSH TO INHIBIT, a monitor light labeled GPWS INOP. In addition, the warning is audible through the pilots' interphone speakers.
C. Primary power for the system is 115 volts ac supplied from the essential flight instrument bus in panel P7 through a circuit breaker labeled GROUND PROX WARN CMPTR.
D. The CADC also supplies 26 volts ac as a reference voltage for the altitude rate circuits.
2. Computer
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A. The ground proximity warning computer (GPWC) is rack-mounted on shelf No. 1 of electronic equipment rack E2. The GPWC consists of a logic and power supply module, a comparator and closure warning, audio, voice, glide slope, monitor, and self-test modules. A power transformer and an interference capacitor are also mounted in the rear of the chassis above the electrical connector.
3. Warning Indicator Light (Fig. 1)
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A. Rectangular shaped red warning light labeled GPWS is installed on the pilots' lightshield. The light has a light-test feature which is controlled by the master dim and test switch. Acccess to the bulbs and a fuse within the light assembly is provided by removing the lens cover.
B. The light comes on to provide a visual indication that the GPWC has generated a warning of an unsafe flight path.
4. Advisory Light
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A. A rectangular shaped amber advisory light labeled BELOW G/S is
installed on the pilots' lighshield. Access to the bulbs and a
fuse is provided by removing the lens cover.
B. The light comes on to provide a visual indication that the airplane is below the glide slope beam when an ILS frequency is selected and the landing gears are down. The warning light has a steady illumination.
5. GPWS Test Switch
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A. The GPWS TEST switch is located on the center instrument panel. It provides a confidence check of the system either on ground or in flight.
6. GPWS Inhibit Switch
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AIRPLANES WITH SUNDSTRAND CONFIG 2 MARK II COMPUTERS 03 Page 1 Apr 25/85
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PILOT'S LIGHTSHIELD FLIGHT ENGINEER'S
SEE A INSTRUMENT PANEL SEE C
CENTER INSTRUMENT PANEL
SEE B
GROUND PROXIMITY WARNING COMPUTER E-2 RACK SHELF NO. 1
PUSH
BELOW
TO
GPWS
G/S
INHIBIT
A
GROUND
GPWS
PROXIMITY
INOP
TEST BC Ground Proximity Warning System Component Location Figure 1
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AIRPLANES WITH SUNDSTRAND CONFIG 2
MARK II COMPUTERS 799 Page 2
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Apr 25/85
A. The G/S inhibit switch is located on the pilot's lightshield. The switch will inhibit the glide slope warning and cancels the advisory light when pressed. The switch is labeled PUSH TO INHIBIT.
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